This invention relates generally to radio-frequency (rf) power combiners and dividers, and more specifically, to combiners and dividers for use in the millimeter-wave frequency band. Higher powers at these frequencies can be obtained by combining the outputs of such devices as diodes that employ impact-ionization and trasit-time properties (IMPATT diodes). There is a need for a power combiner operable over a wide band of millimeter-wave frequencies and capable of handling high powers. Other applications, such as phased-array antennas, require a power dividing function, in which a single high-power rf input signal is to be split into a number of output signals, usually of equal but smaller powers.
Devices available to perform a power combining function include Kurokawa-type combiners, magic tee hybrid couplers and microstrip power dividers or combiners. The Kurokawa devices, named after K. Kurokawa, are well known in the waveguide field. Basically, a Kurokawa device includes a cavity to which are coupled a number of coaxial waveguides providing separate power inputs, such as from IMPATT diodes. Although devices of the Kurokawa type work satisfactorily in some applications, their chief limitation is a relatively narrow bandwidth, arising from their resonant nature.
Magic tee or hybrid couplers have relatively good bandwidth characteristics. Each tee combines two signals into a single output, but the arrangement has significant limitations. There is a practical limitation of four to eight input sources that may be combined. More importantly, for use in the millimeter-wave band of frequencies, these couplers have high loss.
Microstrip combiners or dividers employ combinations of microstrip structures, each consisting of a conductive strip disposed on a dielectric sheet separating the strip from a ground plane. The chief limitation of microstrip structures intended for use as power combiners or dividers is that they have relatively high losses at millimeter-wave frequencies, and are therefore incapable of handling high powers at these frequencies.
Radial line combiners using microstrip structures have been disclosed in U.S. Pat. Nos. 4,371,845 to Pitzalis, Jr., 4,234,854 to Schellenberg et al., and 4,032,865 to Harp et al. Other attempts to produce a wideband non-resonant power combiner structure include a so-called radial line combiner, disclosed in U.S. Pat. No. 3,582,813 to Hines, in which solid-state power-generating devices are disposed around a central coaxial output line, to which they are coupled. Another proposed solution to the problem is the conical power combiner disclosed in U.S. Pat. No. 4,188,590 to Harp et al.
It will be appreciated from the foregoing that there is still a significant need for a power combiner and divider capable of operation at high powers and over a wide band of frequencies in the millimeter-wave band. Ideally, the combiner/divider should have relatively low losses and should couple to standard rectangular waveguides used in millimeter-wave applications. The present invention meets these requirements.